Rolling mills are basically formed of at least two vertically displaced rolls positioned within a relatively large housing for containing the roll at their ends. In general, the lower roll is stationary within the housing, while the upper roll is vertically displaceable both toward and away from the lower roll so as to provide for a variable gap between the rolls, thereby producing a product to desired dimensions. Movement of the upper roll is affected through its chock supports through either hydraulic means or a screw-down mechanism operable to bias and move the upper roll toward the lower roll. The forces necessary to move the upper roll downward toward the lower roll and retain the same during the rolling process are enormous in size. Moreover, the forces necessary to counteract the large downwardly directed upper roll forces in order to keep the upper roll in a given position for any period of rolling time are also relatively large and are effected through the use of steelyard rods and support mechanisms to be described below.
The support structure for the upper roll includes steelyard rods which pass from below the housing structure upwardly to engagement with a portion of the chock on either side of the roll. Positioned below the housing and acting as a terminus for each of the steelyard rods is a separator assembly which extends from one set of steelyard rods across to the other set. The separator acts as a rigid support mechanism for the four steelyard rods and as a linkage mechanism for two large counterweight balances positioned below the roll mill housing. The counterweights act through the separator assembly and the steelyard rods to provide an upward counter-balancing force against the downward force upon the upper roll to retain the upper roll in a given desired position. The counterweights are unbalanced due to the fact that there is provided a drive side for the rolls as well as a non-drive side. The drive side incorporates the drive spindles and, accordingly, the counterweight on the drive side of the rolls is either heavier or has a larger moment arm than the non-drive or operator side of the rolls. This unbalanced counterweight situation results in a varying horizontal thrust through the separator assembly as the separator assembly is moved from its low position to its upper position corresponding to the lower position of the roll (its closed position) and the fully open position of the rolls. This horizontal thrust may vary excessively so that there is a resultant horizontal thrust of between .+-.5,000 to 8,000 pounds in either direction. It is obvious that this resultant horizontal thrust will cause undesireable stresses and forces to the mill housing, to the steelyard rods, the separator, and ultimately, affect the rolling power of the two vertically displaced rolls themselves.
The horizontal thrust noted above also causes undesirable wear in the mill housing holes through which the steelyard rods are passed in their extension from below the mill housing to the roll chock of the upper roll. Due to the horizontal loading of the roll balance system noted above, the steelyard rods wear out in the cast hole of the housing and cause an interference problem inasmuch as they are two piece sections. This interference problem causes the steelyard rods to wear out and necessitates their replacement or may cause a jamming effect which may cause the mill housing to fracture thereby resulting in mill down time.